Geological maps and their interpretation / Геологические карты и их интерпретация

As a preliminary to the detailed reading of a geological map to determine the succession and structure, it is useful to look first at the broad topographical features, including valleys, ridges, and summits. The position of steeper and flatter slopes will be apparent from contours, when these are given, and geological boundaries and their relationship to the topography can be followed. This applies particularly to large-scale maps, for instance at 6 inches to a mile.* Straight runs of outcrop given by steeply dipping or vertical beds
indicate the local direction of strike. Horizontal beds have boundaries which reflect the topographic contours.The vee-ing of outcrops in valleys gives clues as to dip directions, which can be sketched on, using dip arrows. Unconformities (if present) can be marked. When dip directions are known, the order or succession of beds can be found. On large-scale maps stratum contours may often be drawn (through the intersections of geological boundaries with topographical contours), and deductions as to dip made from them. Where folds are present the positions of their axial planes may be sketched on the map. In selecting a line for the drawing of a crosssection, one which follows the general direction of dip and crosses the axes of folds will frequently be the most suitable for showing the structures present in the area. <...>